The present invention relates generally to printers and in particular the present invention relates to thermal printers.
Compact disc publishing and replicating systems often use a printer to place a label on the compact disc (CD). Several options are available for printing. One option is to print directly onto the disc using an ink jet printer or a thermal transfer printer.
An important advantage that thermal transfer printers enjoy over inkjet printers used to label CD""s is that they do not require specially coated CD""s to accept the ink from the printing process. Although printable discs are available, they are more expensive than traditional un-coated media. Further, thermal transfer printers can print with greater speed and print on discs prepared with an inexpensive lacquer coating.
A thermal transfer printer typically includes a stationary print head, a ribbon, and assembly to move the CD under the print head. The print head contains an array of thermal elements, and the ribbon is a plastic film with a wax or resin compound deposited on one side. The print head contacts the ribbon during printing, and the ribbon contacts the media. By heating areas of the ribbon, the wax or resin compound is deposited on the media. Printing occurs by moving ribbon and the media at the same rate across the print head, while firing the heating elements in a desired pattern.
The thermal elements of the print head are susceptible to physical damage and have a limited useful life. If an element becomes defective during a print operation, unacceptable print results may occur. Thermal printers are often integrated into a robotic system to automate the printing of a large quantity of media. If print head damage occurs while the robotics is in operation, a large amount of media can be misprinted and rendered scrap.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for identifying defective thermal elements.
The above-mentioned problems with thermal printers and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a thermal transfer printer comprises a thermal print head having a resistive heating element, and a test circuit coupled to selectively test the resistive heating element by comparing a current conducted through the resistive heating element with a reference.
In another embodiment, a thermal transfer printer comprises a drawer to hold a print media, and a thermal transfer print head positioned to print an image on the media using a pigment source. The print head comprises a plurality of resistive thermal elements. A strobe circuit is provided to apply power to the plurality of resistive thermal elements, and a test circuit is coupled to the print head to test a resistance of the plurality of resistive thermal elements.
A method of testing a thermal transfer printer comprises initiating a test operation, measuring a resistive characteristic of a reference thermal element, establishing a threshold resistive characteristic, and measuring a resistive characteristic of a non-reference thermal element. The resistive characteristics of then non-reference thermal element are compared to the threshold resistive characteristic.